Previous serological studies have shown that certain patients infected with Human Immunodeficiency Virus (HIV) may also be infected with the Human T-cell lymphotropic Virus type I (HTLV-1) and /or type II (HTLV-II). In preliminary studies using sera from 629 HIV infected patients we could show that although sexual transmission of HIV-I/HTLV-II certainly occurs intravenous drug abusers (IVDAs) had a much higher seroprevalence of infection than any other AIDS risk group. It could also be shown that Black and Hispanic IVDAs had significantly higher seropositivity rates than whites and that seropositivity increased with age. Unfortunately serological methods cannot distinguish between infection by the two viruses because of their antigenic cross-reactivity. This requires virus isolation with molecular analysis and /or PCR amplification studies. Using a novel co-cultivation method we have successfully isolated HTLV-II from five IVDAs and provirus mapping of the isolates have suggested that there may be some genetic heterogeneity in this family of viruses. PCR amplificaticn methods have been developed which are specific and sensitive for provirus detection in peripheral blood mononuclear cells and using this method we were able to detect HTLV-II infection in an additional eleven IVDAs. We wish to expand on these preliminary findings and propose the following studies. First we will extend our serological studies to a larger study group to allow the identification of a larger number of dually infected patients. This will be followed by PCR amplification studies to specifically identify the HTLV involved. Virus isolation with provirus mapping will be continued to investigate how significant genetic heterogeneity is in the HTLV-II family. Finally we plan a prospective study of the clinical and immunological features of dually infected IVDAs which with specific virus identification may allow a better understanding of their role in human disease.